Step 1: the trailer

This is a trailer from Harbor Freight Tools.

It's their biggest, as far as I can see.  It's a 4'x8', non folding, two wheeled trailer, rated at 1720lbs. At $350 it's a third of my budget!

http://www.harborfreight.com/automotive-motorcycle/trailer-accessories/1720-lb-capacity-super-duty-48-inch-x-96-inch-utility-trailer-with-12-inch-five-lug-wheels-and-tires-94564.html

Somewhat redundantly: it's worth reading the instructions fully, and making sure you clearly understand which bits are which - the side bars look very similar but need to be in the correct positions for everything to work properly.  I built this trailer three times.

It's definitely a good idea to repack the bearings.  These come only marginally greased.  It's messy and fun: